17,710 research outputs found
Electron-beam-sustained discharge revisited - light emission from combined electron beam and microwave excited argon at atmospheric pressure
A novel kind of electron beam sustained discharge is presented in which a
12keV electron beam is combined with a 2.45GHz microwave power to excite argon
gas at atmospheric pressure in a continuous mode of operation. Optical emission
spectroscopy is performed over a wide wavelength range from the vacuum
ultraviolet (VUV) to the near infrared (NIR). Several effects which modify the
emission spectra compared to sole electron beam excitation are observed and
interpreted by the changing plasma parameters such as electron density,
electron temperature and gas temperature.Comment: 10 pages, 9 figure
Methylation Status of Imprinted Genes and Repetitive Elements in Sperm DNA from Infertile Males
Stochastic, environmentally and/or genetically induced disturbances in the genome-wide epigenetic reprogramming processes during male germ-cell development may contribute to male infertility. To test this hypothesis, we have studied the methylation levels of 2 paternally (H19 and GTL2) and 5 maternally methylated (LIT1, MEST, NESPAS, PEG3, and SNRPN) imprinted genes, as well as of ALU and LINE1 repetitive elements in 141 sperm samples, which were used for assisted reproductive technologies (ART), including 106 couples with strictly male-factor or combined male and female infertility and 28 couples with strictly female-factor infertility. Aberrant methylation imprints showed a significant association with abnormal semen parameters, but did not seem to influence ART outcome. Repeat methylation also differed significantly between sperm samples from infertile and presumably fertile males. However, in contrast to imprinted genes, ALU methylation had a significant impact on pregnancy and live-birth rate in couples with male-factor or combined infertility. ALU methylation was significantly high-er in sperm samples leading to pregnancy and live-birth than in those that did not. Sperm samples leading to abortions showed significantly lower ALU methylation levels than those leading to the birth of a baby. Copyright (C) 2011 S. Karger AG, Base
Exploring black hole superkicks
Recent calculations of the recoil velocity in black-hole binary mergers have
found kick velocities of km/s for equal-mass binaries with
anti-aligned initial spins in the orbital plane. In general the dynamics of
spinning black holes can be extremely complicated and are difficult to analyze
and understand. In contrast, the ``superkick'' configuration is an example with
a high degree of symmetry that also exhibits exciting physics. We exploit the
simplicity of this ``test case'' to study more closely the role of spin in
black-hole recoil and find that: the recoil is with good accuracy proportional
to the difference between the modes of , the major
contribution to the recoil occurs within before and after the merger, and
that this is after the time at which a standard post-Newtonian treatment breaks
down. We also discuss consequences of the asymmetry in the
gravitational wave signal for the angular dependence of the SNR and the
mismatch of the gravitational wave signals corresponding to the north and south
poles
Reexamining Black-Body Shifts for Hydrogenlike Ions
We investigate black-body induced energy shifts for low-lying levels of
atomic systems, with a special emphasis on transitions used in current and
planned high-precision experiments on atomic hydrogen and ionized helium.
Fine-structure and Lamb-shift induced black-body shifts are found to increase
with the square of the nuclear charge number, whereas black-body shifts due to
virtual transitions decrease with increasing nuclear charge as the fourth power
of the nuclear charge. We also investigate the decay width acquired by the
ground state of atomic hydrogen, due to interaction with black-body photons.
The corresponding width is due to an instability against excitation to higher
excited atomic levels, and due to black-body induced ionization. These effects
limit the lifetime of even the most fundamental, a priori absolutely stable,
"asymptotic" state of atomic theory, namely the ground state of atomic
hydrogen.Comment: 11 pages; LaTe
The five-minute oscillations: What's left to be done
Current observational methods for studying these oscillations at large horizontal wavenumbers are discussed in detail and several two dimensional power spectra obtained with a CID camera on the main spectrograph of the McMath telescope at Kitt Peak National Observatory are described. The best-resolved observations of the p-mode obtained at chromospheric elevations are also presented. Recent progress in studies of the p-modes at low wavenumbers with full-disk velocity detection schemes is summarized. These full-disk observations of radial and low-degree non-radial modes were shown to place severe constraints on the theoretical calculation of solar interior structure. Progress in making fully-consistent solar models which fit both the high- and low-wave number observations is described. Finally, the observational and theoretical improvements that are necessary for further progress in solar seismology are summarized
Alloreactive cytotoxic T lymphocytes generated in the presence of viral- derived peptides show exquisite peptide and MHC specificity
The nature of alloreactivity to MHC molecules has been enigmatic, primarily because of the observation that allogeneic responses are considerably stronger than syngeneic responses. To better determine the specificity potential of allogeneic responses, we have generated alloreactive CTL specific for exogenous, viral-derived peptide ligands. This approach allowed us to critically evaluate both the peptide- and MHC-specificity of these alloreactive T cells. Exploiting the accessibility of the H-2Ld class I molecule for exogenous peptide ligands, alloreactive CTL were generated that are specific for either murine cytomegalovirus (MCMV) or lymphocytic choriomeningitis virus (LCMV) peptides bound by Ld alloantigens. Peptide specificity was initially observed in bulk cultures of alloreactive CTL only when tested on peptide-sensitized T2.Ld target cells that have defective presentation of endogenous peptides. Subsequent cloning of bulk alloreactive CTL lines generated to MCMV yielded CTL clones that had exquisitely specific MCMV peptide recognition requirement. All of the MCMV/Ld alloreactive CTL clones were also exquisitely MHC-specific in that none of the CTL clones lysed targets expressing MCMV/Lq complexes, even though Lq differs from Ld by only six amino acid residues and Lq also binds the MCMV peptide. This observation clearly demonstrates that alloreactive CTL are capable of the same degree of specificity for target cell recognition as are syngeneic CTL in MHC-restricted responses
Anomalous oxygen isotope effect on the in-plane FIR conductivity of detwinned YBa2Cu3O
We observe an anomalous oxygen isotope effect on the a-axis component of the
far-infrared electronic response of detwinned YBa2Cu3O. For
O a pronounced low-energy electronic mode (LEM) appears around 240
cm. This a-axis LEM exhibits a clear aging effect, after one year it is
shifted to 190 cm. For O we cannot resolve a corresponding a-axis
LEM above 120 cm. We interpret the LEM in terms of a collective
electronic mode that is pinned by `isotopic defects', i.e. by the residual
O in the matrix of O.Comment: 10 pages, 2 figure
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